There is a need in the field of water purification to remove chlorite ion from water prior to use or the disposing of the water in order to make the disposed water non-toxic. Several methods of removing the chlorite ion have been found. These methods all suffer from drawbacks in that pH adjustment is needed, sludge production occurs, or some other drawback results.
The chlorite ion is toxic to several invertebrates which are important in the food chain. Chlorine dioxide (ClO2) in disinfection and other applications results in chlorite ion in the water. When this water flows to a receiving stream or other body of water, chlorite must be reduced to very low levels to meet government regulations.
Chlorite removal is difficult. Known chlorite removal chemistries are slow, produce sludge, require precise pH control or produce unwanted by-products.
Current regulations in some locations require chlorite ion to be at or below 0.006 mg/L in water entering receiving streams; in other locations the amount of chlorite entering the stream may be higher. The dosage of chlorine dioxide (ClO2) is typically 0.5-1.0 mg/L above demand (which can be higher with 2.0 mg/L being typical). For a demand of 2.0 mg/L, an applied dosage of 2.5-3.0 mg/L ClO2 is used. Approximately 50-80% of the applied dosage of ClO2 is ultimately converted to chlorite ion. If 3.0 mg/L is fed, 1.5-2.4 mg/L of chlorite ion can be produced. This amount varies depending upon water conditions. Since many of these systems are once-through, the water velocity is such that any treatment must act quickly and completely to remove chlorite before discharge. Therefore, any treatment must reduce chlorite levels to essentially immeasurable levels of innocuous species in a few seconds. The treatment itself must also be innocuous, in the event of over treatment.